Diesel engine exhaust systems include particulate filters, catalyst soot filters, and NOx adsorber catalysts that clean exhaust and reduce engine emissions. There is a need to regenerate and desulfate exhaust system components on a regular basis for efficient operation.
Regeneration of diesel particulate filters requires heating the filters to temperatures of approximately 500° C. for a period of about 10 minutes. Regeneration of catalyzed soot filters requires heating the filters to temperatures of approximately 400° C. for a period of about 10 minutes. Desulfation of NOx adsorbers requires heating the catalysts to temperatures of approximately 700° C. for at least 5 minutes while operating the engine with a rich air/fuel mixture (excess fuel/no excess oxygen), that produces exhaust gas with higher concentrations of unburned hydrocarbons and carbon monoxide, and no oxygen. The prior art has proposed maintaining high catalyst temperatures by locating the catalyst components close to the engine turbocharger turbine outlet. This approach is not practical in on-highway vehicles due to space constraints.
In the past, active regeneration of the filters has been employed to regenerate compression ignition engine exhaust filters and catalysts. The preferred way to perform an active regeneration cycle is to heat the filter and catalyst components while the vehicle is at rest, for example, during a refueling stop. High exhaust temperatures are most effectively generated by loading the engine. However, it is difficult to adequately load an engine while a vehicle is at rest. The only loads on the engine when a vehicle is at rest are electrical loads such as those associated with lights and air conditioning systems and mechanical loads related to the operation of an air compressor, cooling fan and the idling torque load of the engine. These loads are negligible compared to the road loads encountered when a loaded vehicle is climbing a grade.
There is a need for an effective system for altering fuel/air ratios to effect a passive regeneration of a compression ignition engine exhaust system.
There is a need for an effective system for producing higher temperatures needed for passively regenerating exhaust system filter and catalyst components without unduly penalizing fuel economy.
There is a need for an effective system for altering engine operating parameters, such as, for example, fuel ignition timing and/or NOx/Particulate Material ratio maps to effect a passive regeneration of engine exhaust filters and catalysts.
These and other problems are addressed by applicant's invention and summarized below.